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Vitamin D could play a role in insulin production.
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New research suggests that vitamin D supplementation may be linked to a lower risk of diabetes for some people.
The benefit appears to be limited to certain individuals with prediabetes who have a specific genetic variation.
Vitamin D should be taken under a doctor’s guidance and not replace proven strategies for diabetes prevention.
More than two in five adults in the United States have prediabetes, a condition in which blood sugar levels are higher than normal. Having prediabetes increases the risk of developing type 2 diabetes—but a new study suggests that, for many people, supplementing with vitamin D may help cut that risk.
The study, published in the journal JAMA Network Open, found that people with a certain genetic variation may be more likely to benefit from vitamin D.
The findings don’t prove that vitamin D itself lowers diabetes risk in this group, but they “may represent an important step in developing a more personalized approach [to treatment] through genetics,” said Anastasios Manessis, MD, FACE, ABOM, a double board-certified endocrinologist and obesity medicine physician at Endocrine Associates of West Village, who wasn’t involved in the new research.
A Deeper Look Into Vitamin D and Diabetes Risk
For the new study, researchers drew on data from a 2019 trial known as the D2d study. That research found no meaningful reduction in diabetes risk among roughly 2,100 participants with prediabetes who took 4,000 international units (IU) of vitamin D3—a form that is more effective at raising vitamin D levels—daily for four years, compared with those taking a placebo.
In the 2026 analysis, however, researchers took a closer look at the data, digging in to see whether certain subgroups within the vitamin D group benefitted more than others. They found that participants whose vitamin D levels reached a certain threshold—40 to 50 ng/mL—had a substantially lower risk of developing type 2 diabetes.
The team suspected that genetic variations in vitamin D receptors might influence how effectively the body responds to the vitamin. These receptors help cells use vitamin D from the bloodstream and are found throughout the body, including in the pancreas’s beta cells, which produce insulin. If vitamin D is working effectively, it’s believed that it may help protect against diabetes by keeping those cells functional and efficient, explained Gillian Goddard, MD, a board-certified endocrinologist and adjunct assistant professor at NYU Grossman School of Medicine who was also not involved with the research.
To investigate their hypothesis, researchers grouped participants based on three common genetic variations in the vitamin D receptor: AA, AC, and CC.
After analysis, they found that those with the AA variation of the Apal vitamin D receptor gene—about 30% of the study population—saw no significant difference compared with placebo. In contrast, the roughly 70% of participants with the AC or CC variations had a 19% lower risk of type 2 diabetes.
Should You Take Vitamin D to Prevent Diabetes?
While the authors noted that their findings “hold promise” for vitamin D3 as a “targeted, personalized approach” to lowering type 2 diabetes risk for some people, they cautioned that the results need to be confirmed by more research. One limitation, they added, is that the study didn’t examine whether genetic differences affected outcomes differently across racial or ethnic groups.
Even if vitamin D could help some people ward off diabetes, though, Goddard warned against supplementing without guidance from a doctor. While vitamin D is generally considered safe, one of the biggest risks is taking too much. Because it’s fat-soluble, excess amounts are stored in the liver and fat tissue rather than flushed out in urine, as with water-soluble vitamins like vitamin C.
Experts recommend 600 IU daily for adults up to age 70 and 800 IU for those over 70, with an upper daily limit of 4,000 IU. Those guidelines account for vitamin D from all sources, including supplements, food, and sun exposure.
Regularly exceeding that amount can lead to hypercalcemia, a condition in which calcium levels in the blood become too high. While it’s usually not life-threatening, hypercalcemia can cause nausea, vomiting, weakness, confusion, and kidney stones. It can also increase the risk of falls and fractures, which Manesiss said is especially concerning for older adults.
What Experts Recommend
Even if you start taking vitamin D, it shouldn’t replace other strategies that are proven to lower the risk of type 2 diabetes.
To help ward of the condition, Goddard recommended following a diet low in carbohydrates and high in fiber and lean protein. Regular exercise—both aerobic and strength training—is also important. “Muscle is better at metabolizing sugar than fat is,” she said.
Certain medications, including metformin and GLP-1s, can also help reduce the risk of diabetes, Goddard added.
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